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Clues to relative distance of different objects Retinal Disparity Diff between the two images Closer the object = the larger the disparity Convergence Degree to which eyes face inward Closer the object = the greater convergence

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Binocular Cues Retinal/Binocular disparity: Images from the two eyes differ. Try looking at your two index fingers when pointing them towards each other half an inch apart and about 5 inches directly in front of your eyes. You will see a “finger sausage” as shown in the inset. http://www.michaelbach.de/ot/sze_Frankfurter/index.html http://www.netaxs.com/~mhmyers/rds-ex.html Stereograms

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Perceptual Constancy Objects remain unchanged as their image on the retina changes Shape Constancy Size Constancy – looking at the same size objects close and far away –Close Object –> projects larger image on our retina. –Far Object –> projects smaller image on our retina. Example: as a person walks away from you their retinal image decreases in size. However, we know that they are just getting farther away not shrinking in size.

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Relative Size Interposition If two objects are similar in size, we perceive the one that casts a smaller image to be farther away If one object partially blocks our view of another object, we perceive it as closer Monocular Cues

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Texture Gradient Linear Perspective Indistinct (fine) texture signals an increasing distance, while coarse texture signals a close distance. Monocular Cues Parallel lines appear to converge in the distance. The more the lines converge, the greater their perceived distance.

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Relative Height Relative Motion We perceive objects that are higher in our field of vision to be farther away than those that are lower. Monocular Cues Objects closer to (in front of )a fixation point move faster and in opposing direction to those objects that are farther away from (behind) a fixation point, moving slower and in the same direction.

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Optical Illusion: Ponzo The distant monster (below, left) and the top red bar (below, right) appear bigger because of size constancy and the monocular distance cues of linear perspective and texture gradient. Linear Perspective - parallel lines appear to converge in the distance. The more the lines converge, the greater their perceived distance Texture Gradient – indistinct (fine) texture signals an increasing distance, while coarse texture signals a close distance Size Constancy - If 2 objects cast identical retinal images (i.e., they are the same size), the object appearing further away is perceived as larger and so the brain perceptually enlarges the image

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Optical Illusion: Horizontal- Vertical Illusion The vertical line appears longer than the equally long horizontal line because of size constancy and the monocular distance cue of relative height Relative height – Objects at the top of our visual field appear to be more distant. Size constancy - If 2 objects cast identical retinal images (i.e., they are the same size), the object appearing further away is perceived as larger and so the brain perceptually lengthens the vertical line.

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Optical Illusion: Muller-Lyer (a) Outward pointing arrows signify that the top horizontal line is farther and thus looks longer; while (b) inward pointing arrows signify that the horizontal line is closer and thus looks shorter. The illusion is not cross-cultural. Non-Western subjects, and particularly subjects whose day-to- day surroundings are usually not rectangular (few buildings, doors, walls) are much less likely to be affected by it

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Perceptual Organization Max Wertheimer (1880-1943) “The whole is different than the sum of its parts.” Gestalt Psychology Described principles by which we organize sensations into perceptions. create We combine bottom-up info with top-down knowledge to create perception http://www.thepsychfiles.com/2007/10/episode-31- lemon-slices-and-a-new-face-on-mars-gestalt- principles-at-work/

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Principles of Gestalt Psychology Proximity (group nearby figures together)  Similarity (group figures that are similar)  Figure & Ground (organization of the visual field into objects (figures) that stand out from their surroundings (ground))

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Proximity Perceiving objects close to each other as forming a group. Looking at the picture, since the horizontal rows of circles are closer together than the vertical columns, we perceive two vertical lines. Since the first two columns and the last two columns have less space between them than the center two columns, we perceive two groups of two columns.

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Closure The principle of closure applies when we tend to see complete figures even when part of the information is missing. Closing up or completing figures that are not, in fact, complete We see three black circles covered by a white triangle, even through it could just as easily be three incomplete circles joined together. Our minds react to patterns that are familiar, even though we often receive incomplete information. It is speculated this is a survival instinct, allowing us to complete the form of a predator even with incomplete information.

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Continuation Perceiving smoothly flowing or continuous forms rather than disrupted or discontinuous ones. As seen in the example, we perceive the figure as two crossed lines instead of 4 lines meeting at the center. Even though the circle is not joined together, we still perceive a circle due to the principle of closure

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Similarity The principle of similarity states that things which share visual characteristics such as shape, size, color, texture, value or orientation will be seen as belonging together. In the example, the two filled lines gives our eyes the impression of two horizontal lines, even though all the circles are equidistant from each other. In the example, the larger circles appear to belong together because of the similarity in size.

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Observer Characteristics: Experience / Culture 24 To an East African, the woman sitting is balancing a metal box on her head, while the family is sitting under a tree. The predominating norms, behavior patterns, artifacts, institutions, and attitudes of a group of people. In addition, past learning shapes perception.

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Observer Characteristics: Expectations Preconceptions about what we are supposed to perceive may also influence perception by causing us to delete, insert, transpose, or otherwise modify what we see. Perceptual familiarization/generalization - strong tendency to see what we expect to see even if our expectation conflicts with external reality. Perceptual set - a readiness to perceive a stimulus in a particular way. Schemas -mental framework that organizes and interprets information Context Effects - immediate context of a figure influences one’s perception of it.

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Expectations: Context Effects Olny srmat poelpe can. I cdnuolt blveiee that I cluod aulaclty uesdnatnrd waht I was rdanieg. The phaonmneal pweor of the hmuan mnid, aoccdrnig to rscheearch at Cmabridgde Uinervtisy, it deosn’t mttaer in what oredr the ltteers in a word are, the olny iprmoatnt tihng is that the frist and lsat ltteer be in the rghit pclae The rset can be a taotl mses and you can still raed it wouthit a porbelm. This is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the word as a wlohe. Amzanig huh? Yaeh and I awlyas tghuhot slpeling was ipmorantt! 26 We interpret what we see based on the context in which we see it (first and last letter of word).

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Expectations: Context Effects Dear Mother and Dad: Since I left for college I have been remiss in writing and I am sorry for my thoughtlessness in not having written before. I will bring you up to date now, but before you read on, please sit down. You are not to read any further unless you are sitting down, okay? Well, then, I am getting along pretty well now. The skull fracture and the concussion I got when I jumped out the window of my dormitory when it caught on fire shortly after my arrival here is pretty well healed now. I only spent two weeks in the hospital and now I can see almost normally and only get those sick headaches once a day. Fortunately, the fire in the dormitory, and my jump, was witnessed by an attendant at the gas station near the dorm, and he was the one who called the Fire Department and the ambulance. He also visited me in the hospital and since I had nowhere to live because of the burntout dormitory, he was kind enough to invite me to share his apartment with him. It’s really a basement room, but it’s kind of cute. He is a very fine boy and we have fallen deeply in love and are planning to get mar­ried. We haven’t got the exact date yet, but it will be before my pregnancy begins to show. Yes, Mother and Dad, I am pregnant. I know how much you are looking forward to being grandparents and I know you will welcome the baby and give it the same love and devotion and tender care you gave me when I was a child. The reason for the delay in our marriage is that my boyfriend has a minor infection which prevents us from passing our pre­marital blood tests and I carelessly caught it from him. I know that you will welcome him into our family with open arms. He is kind and, although not well educated, he is ambi­tious. Although he is of a different race and religion than ours, I know your often expressed tolerance will not permit you to be bothered by that. Now that I have brought you up to date, I want to tell you that there was no dormitory fire, I did not have a concussion or skull fracture, I was not in the hospital, I am not pregnant, I am not engaged, I am not infected, and there is no boyfriend. However, I am getting a “D” in American History, and an “F” in Chemistry and I want you to see those marks in their proper perspective. Your loving daughter, Sharon

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Expectations: Schemas Provide punctuation that will make the following words meaningful: TIME FLIES I CANT THEYRE TOO FAST The apostrophes come easily, but the rest is difficult. TIME FLIES. I CAN’T. THEY’RE TOO FAST. It still does not seem to make sense because we’re too familiar with the slogan, “Time flies” in which “time” is a noun and “flies” is a verb. Tell students to read “time” as the verb and “flies” as the noun. It now makes perfect sense. 29

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Observer Characteristics: Cognitive Style COGNITIVE STYLE: Way of processing the stimuli within the environment, which affects how we see the world. Pg. 454 H:3-4 Demo –Field-dependent approach = perceive the environment as a whole and do not clearly distinguish in their minds the shape, color, size, or other qualities of individual items. No details. “Levelers” –Field-independent approach = perceive the elements of the environment as separate and distinct from one another and to draw each element as standing out from the background. A lot of details. “Sharpeners”

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Observer Characteristics VALUES: What we deem as important will shape our perceptions. PERSONALITY: Person’s unique pattern of thoughts, feelings, and behaviors affect perception. MOTIVATION: Our desires and needs strongly shape our perceptions. People in need are more likely to perceive something that they think will satisfy that need.

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